1. Field of the Invention
The invention relates to the formation of gel beads, more particularly, the invention relates to the formation of gel beads using an atomizer.
2. Statement of the Related Art
The literature is replete with references to the production of hydrocolloid microparticles. Many techniques have been used to prepare hydrocolloid microparticles, such as spray processes and emulsion processes. Other references related to the production of gel beads includes the following:
James C. Ogbonna et al., "Production of Micro-Gel Beads by a Rotating Disk Atomizer," Journal of Fermentation and Bioengineering, Vol. 68, No. 1, pp. 40-48, 1989 teaches the production of micro-gel beads having a 200-1200 micron diameter by the atomization of an alginate with a rotating disk.
H. Suet al., "Characterization of Alginate Beads Formed by a Two Fluid Annular Atomizer," Applied Biochemistry and Biotechnology, Vol. 20/21, pp. 561-569, 1989, teaches the use of a two fluid atomizer to prepare alginate beads having a mean diameter in the range of 50-500 microns.
Antonio R. Navarro et al., "Production of Ethanol by Yeasts Immobilized in Pectin," European Journal of Applied Microbiology and Biotechnology, Vol 17, pp. 148-151, 1983, teaches the formation of pectin beads by pumping a pectin solution through a hypodermic needle to form drops which are received in a mixture of CaCl.sub.2.2H.sub.2 O and Na.sub.2 B.sub.4 O.sub.7. 10H.sub.2 O, with the bead diameter being a function of the rate of extrusion and the diameter of the hypodermic needle.
R. M. Buitelaar et al., "Immobilization of Biocatalysts in Thermogels Using the Resonance Nozzle for Rapid Drop Formation and an Organic Solvent for Gelling," Biotechnology Techniques, Vol. 2, No. 2, pp. 109114 (1988) teaches the formation of gel beads using either a resonance needle for rapid drop formation or a needle dripping technique which also produces gel beads. K-carrageenan is taught as a gellant.
Stemberg et al. (U.S. Pat. No. 3,639,306) disclose the formation of particulates using a dual spray nozzle making small particulates, by spray drying materials into a fluidized bed.
Wang et al. (U.S. Pat. No. 4,645,442) disclose a nozzle structure, useful for making gas-filled microspheres.
Seaget (U.S. Pat. No. 4,016,254) discloses making microcapsules by spray drying, using concurrent air flow. Shioya et al. (U.S. Pat. No. 4,814,274) disclose making encapsulated bodies, in which a stream of pressurized air is exterior to a stream of gellable solution.
Other work in this field has been conducted by Frosch et al. (U.S. Pat. No. 4,279,632), Beggs et al. (U.S. Pat. No. 4,344,787), Torobin (U.S. Pat. No. 4,671,909), Schlameus et al. (U.S. Pat. No. 4,888, 140), and Friend (U. S. Pat. No. 5,091,122).
In addition the following references describe methods for encapsulating other materials within the microparticles.
British patent No. 887,901 to F. Hoffman-La Roche & Co. (CA 56, 9179 i(1961 )) discloses emulsions of a gelling colloid, including pectin and algin, which are dried into particles by spraying or atomizing into a gas at least 10.degree. below the t.sub.m of the resultant gel, and the particles are kept separate in free fall for at least 15 seconds for gelling to begin.
U.S. Pat. No. 2,438,450 to Nelson discloses a drying technique for microparticulates comprising mixing with the hydrated micropadiculates a quantity of previously dried microparticulates to prevent agglomeration of the hydrated microparticles.
V. Ghetie and H. D. Schell, "Drying of Agarose Gel Beads", Experientia 27(12), 1384-5, 1971 discloses agarose microparticles which are acetone washed, then air dried at room temperature.
In addition to the above specialized drying techniques for minimizing agglomeration problems, the techniques have been used to try to prevent agglomeration of hydrocolloid microparticles. For example, U.S. Pat. No. 5, 153,020 to Singer et al., discloses water-dispersible spheroidal macrocolloid microparticles as a fat substitute with which "aggregate blocking agents," such as lecithin, pectin, xanthan gum, and carboxymethylcellulose, are added to the macrocolloid particles to stabilize the particles in the hydrated form in which the particles are manufactured and employed as fat substitutes.
U.S. 4,911,946 discloses the use of aggregate blocking agents such as lecithin and xanthan gum in hydrated spheroidal carbohydrate microparticles to, produce the mouth feel of fat/cream.
The following references disclose microparticles containing an inner core which can be a hydrocolloid, and an outer hydrophobic coating of a digestible fat: U.S. Pat. No. 4,305,964; EP-A0 011 345; and EP-A0 380 225.
U.S. Pat. No. 3,527,712 discloses a process of preparing chromatography-size agarose beads by including within an agarose gel a macromolecular hydrocolloid such as sodium alginate, potassium lambda carrageenan, carrageenan, hydroxymethylcellulose, sodium carboxymethylcellulose, and the like. Upon drying the agarose beads the macromolecular hydrocolloid becomes coagulated within the pore of the agarose. Upon rehydration, the macromolecular hydrocolloid dissolves, leaving the porosity of the gel substantially intact for its intended use in chromatography.
U.S. 4,952,686 to Rennet al. discloses an alloy gum of cassia gum and a gelling and thickening agent such as carrageenan, agar, agarose, hydroxyethylcellulose, carboxymethylceulose, dextran, and the like. This alloy gum when dried and ground into a powder can be readily dissolved in water to form a clear, stable colloidal solution.
Japanese patent publication 04/08,257 (92/08,257) (CA 116: 172746C) discloses the manufacture of dry konjac, which can be soaked in water to restore its original state and organoleptic properties, by mixing konjac with mono- and/or oligosaccharides such as glucose, sucrose, maltose, lactose and fructose, and then drying the mixture.
WO 91/19424 (PCT published application) discloses hydrated microparticulate beads as a fat substitute composed of a hydrous hydrocolloid gel, a metal capable of causing gellation, and an ionic polysacchadde such as alginate, pectate, and sodium carboxymethyl cellulose.
None of these references teaches the production of hydrocolloid microbeads having a mean particle size of less than 50 microns; in particular, none teaches the large scale production of such micro-gel beads. Such has been considered not to be a practical product. This is perhaps not surprising since gel-forming hydrocolloid microparticles exhibit very strong propensities to aggregate when wet or even in the presence of limited moisture such as when the dry microparticles are stored in contact with air. This propensity becomes even more pronounced as the particles decrease in size.
Furthermore, microparticulates made from gel-forming hydrocolloid alone cannot be dried and then rehydrated without specialized drying techniques to prevent agglomeration, since the dried agglomerates will not disperse or will disperse very poorly in the presence of water upon attempted rehydration. Agglomerated micropadiculates cannot be used as a fat substitute since they do not possess the required organoleptic properties. It is therefore essential that dried microparticulates be capable of rehydration to their original size and shape in order to closely mimic the organoleptic properties of fat, especially in oil-in-water emulsions. This problem of agglomeration when rehydrated is not shared, or is shared to only a limited extent, with larger size hydrocolloid particles such as those disclosed in U.S. Pat. No. 3,527,712 and U.S. Pat. No. 4,952,686.